ld: Add --enable-separate-code

This patch adds --enable-separate-code to ld configure to turn on
-z separate-code by default and enables it by default for Linux/x86.
This avoids mixing code pages with data to improve cache performance
as well as security.

To reduce x86-64 executable and shared object sizes, the maximum page
size is reduced from 2MB to 4KB when -z separate-code is turned on by
default.  Note: -z max-page-size= can be used to set the maximum page
size.

We compared SPEC CPU 2017 performance before and after this change on
Skylake server.  There are no any significant performance changes.
Everything is mostly below +/-1%.

bfd/

	* config.in: Regenerated.
	* configure: Likewise.
	* configure.ac: Add --enable-separate-code.
	(DEFAULT_LD_Z_SEPARATE_CODE): New AC_DEFINE_UNQUOTED.  Default
	to 1 for Linux/x86 targets,
	* elf64-x86-64.c (ELF_MAXPAGESIZE): Set to 0x1000 if
	DEFAULT_LD_Z_SEPARATE_CODE is 1.

ld/

	* NEWS: Mention --enable-separate-code.
	* configure.ac: Add --enable-separate-code.
	(DEFAULT_LD_Z_SEPARATE_CODE): New AC_DEFINE_UNQUOTED.
	* configure.tgt: Default ac_default_ld_z_separate_code to 1 for
	Linux/x86 targets.
	* config.in: Regenerated.
	* configure: Likewise.
	* emultempl/elf32.em (gld${EMULATION_NAME}_before_parse): Set
	link_info.separate_code DEFAULT_LD_Z_SEPARATE_CODE.

5 files changed, 79 insertions, 4 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 5c2a888..59f7c9c 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,13 @@
+2018-02-27  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* config.in: Regenerated.
+	* configure: Likewise.
+	* configure.ac: Add --enable-separate-code.
+	(DEFAULT_LD_Z_SEPARATE_CODE): New AC_DEFINE_UNQUOTED.  Default
+	to 1 for Linux/x86 targets,
+	* elf64-x86-64.c (ELF_MAXPAGESIZE): Set to 0x1000 if
+	DEFAULT_LD_Z_SEPARATE_CODE is 1.
+
 2018-02-27  Nick Clifton  <nickc@redhat.com>
 
 	* aout-cris.c (swap_ext_reloc_out): Standadize error/warning
diff --git a/bfd/config.in b/bfd/config.in
index 75a5ff0..186741d 100644
--- a/bfd/config.in
+++ b/bfd/config.in
@@ -10,6 +10,10 @@
 /* Name of host specific core header file to include in elf.c. */
 #undef CORE_HEADER
 
+/* Define to 1 if you want to enable -z separate-code in ELF linker by
+   default. */
+#undef DEFAULT_LD_Z_SEPARATE_CODE
+
 /* Define to 1 if translation of program messages to the user's native
    language is requested. */
 #undef ENABLE_NLS
diff --git a/bfd/configure b/bfd/configure
index 6c2b24e..d1fe335 100755
--- a/bfd/configure
+++ b/bfd/configure
@@ -793,6 +793,7 @@ enable_targets
 enable_64_bit_archive
 with_mmap
 enable_secureplt
+enable_separate_code
 enable_leading_mingw64_underscores
 with_separate_debug_dir
 with_pkgversion
@@ -1446,6 +1447,7 @@ Optional Features:
   --enable-targets        alternative target configurations
   --enable-64-bit-archive force 64-bit archives
   --enable-secureplt      Default to creating read-only plt entries
+  --enable-separate-code  enable -z separate-code in ELF linker by default
   --enable-leading-mingw64-underscores
                           Enable leading underscores on 64 bit mingw targets
   --enable-werror         treat compile warnings as errors
@@ -11428,7 +11430,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11431 "configure"
+#line 11433 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -11534,7 +11536,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11537 "configure"
+#line 11539 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12171,6 +12173,33 @@ $as_echo "#define USE_SECUREPLT 1" >>confdefs.h
 
 fi
 
+# Decide if -z separate-code should be enabled in ELF linker by default.
+ac_default_ld_z_separate_code=unset
+# Check whether --enable-separate-code was given.
+if test "${enable_separate_code+set}" = set; then :
+  enableval=$enable_separate_code; case "${enableval}" in
+  yes) ac_default_ld_z_separate_code=1 ;;
+  no) ac_default_ld_z_separate_code=0 ;;
+esac
+fi
+
+# Enable -z separate-code by default for Linux/x86.
+case "${target}" in
+i3-786-*-linux-* | x86_64-*-linux-*)
+  if test ${ac_default_ld_z_separate_code} = unset; then
+    ac_default_ld_z_separate_code=1
+  fi
+  ;;
+esac
+if test "${ac_default_ld_z_separate_code}" = unset; then
+  ac_default_ld_z_separate_code=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define DEFAULT_LD_Z_SEPARATE_CODE $ac_default_ld_z_separate_code
+_ACEOF
+
+
 # Check whether --enable-leading-mingw64-underscores was given.
 if test "${enable_leading_mingw64_underscores+set}" = set; then :
   enableval=$enable_leading_mingw64_underscores;
diff --git a/bfd/configure.ac b/bfd/configure.ac
index 2342f3f..20e2c02 100644
--- a/bfd/configure.ac
+++ b/bfd/configure.ac
@@ -97,6 +97,30 @@ if test $use_secureplt = true; then
     [Define if we should default to creating read-only plt entries])
 fi
 
+# Decide if -z separate-code should be enabled in ELF linker by default.
+ac_default_ld_z_separate_code=unset
+AC_ARG_ENABLE(separate-code,
+	      AS_HELP_STRING([--enable-separate-code],
+	      [enable -z separate-code in ELF linker by default]),
+[case "${enableval}" in
+  yes) ac_default_ld_z_separate_code=1 ;;
+  no) ac_default_ld_z_separate_code=0 ;;
+esac])
+# Enable -z separate-code by default for Linux/x86.
+case "${target}" in
+i[3-7]86-*-linux-* | x86_64-*-linux-*)
+  if test ${ac_default_ld_z_separate_code} = unset; then
+    ac_default_ld_z_separate_code=1
+  fi
+  ;;
+esac
+if test "${ac_default_ld_z_separate_code}" = unset; then
+  ac_default_ld_z_separate_code=0
+fi
+AC_DEFINE_UNQUOTED(DEFAULT_LD_Z_SEPARATE_CODE,
+  $ac_default_ld_z_separate_code,
+  [Define to 1 if you want to enable -z separate-code in ELF linker by default.])
+
 AC_ARG_ENABLE(leading-mingw64-underscores,
   AS_HELP_STRING([--enable-leading-mingw64-underscores],
                  [Enable leading underscores on 64 bit mingw targets]),
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index 02a3d37..7016964 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -4942,7 +4942,11 @@ elf_x86_64_special_sections[]=
 #define ELF_ARCH			    bfd_arch_i386
 #define ELF_TARGET_ID			    X86_64_ELF_DATA
 #define ELF_MACHINE_CODE		    EM_X86_64
-#define ELF_MAXPAGESIZE			    0x200000
+#if DEFAULT_LD_Z_SEPARATE_CODE
+# define ELF_MAXPAGESIZE		    0x1000
+#else
+# define ELF_MAXPAGESIZE		    0x200000
+#endif
 #define ELF_MINPAGESIZE			    0x1000
 #define ELF_COMMONPAGESIZE		    0x1000
 
@@ -5335,7 +5339,11 @@ elf64_l1om_elf_object_p (bfd *abfd)
 #undef	ELF_MAXPAGESIZE
 #undef	ELF_MINPAGESIZE
 #undef	ELF_COMMONPAGESIZE
-#define ELF_MAXPAGESIZE			0x200000
+#if DEFAULT_LD_Z_SEPARATE_CODE
+# define ELF_MAXPAGESIZE		0x1000
+#else
+# define ELF_MAXPAGESIZE		0x200000
+#endif
 #define ELF_MINPAGESIZE			0x1000
 #define ELF_COMMONPAGESIZE		0x1000
 #undef	elf_backend_plt_alignment